This invention relates to an inductive angle sensor with a stator element, having an exciting coil with a periodic AC voltage applied thereto and several receiving coils, and with a rotor element that affects a strength of inductive coupling between the exciting coil and receiving coils as a function of its angular position relative to the stator element, and an evaluation circuit for determining the angular position of the rotor element relative to the stator element from voltage signals induced in the receiving coils.
An embodiment of a position sensor shown in FIG. 3 of European patent application (0 159 191 A2) discloses such an angle sensor. A structural principle of this position, or angle, sensor is that secondary coils formed as angularly-periodic, interspaced, series-connected coil sequences are provided, with each coil sequence being formed of one or more pairs of coils connected in reversed polarity. Because of this reversed polarity connection, an output signal coupled in from primary coils to a coil sequence of secondary coils is respectively (approximately) zero.
A movable element, the position of which is to be determined relative to this coil arrangement, has a "flow coupler" that is structured to be small in contrast to dimensions of a measuring path and modifies coupling between the primary coil(s) and individual secondary coils. A coil sequence of secondary coils that contains a secondary coil influenced in this manner generates an output signal that is different from zero. Each of the coil sequences of secondary coils is connected with part of a phase shifting network so that, at an output of this network, an output signal dependent on the position of the movable element is phase shifted relative to the signal fed into the primary coil (s). An evaluation of a time difference between the signal fed into the primary coils and the output signal of the phase shifting network is used for determining a respective position of the movable element. In European patent document (EPA 0 159 191 A2), a magnetic element that is small relative to the measuring path or even a conducting ring (page 4, paragraph 2) is suggested as a flow coupler; the ring is characterized as disadvantageous since it produces only a weak output signal.
Use of a phase shifting network, whose tolerances significantly reduce a measuring accuracy of the sensor, is disadvantageous in this angle sensor. The zero output signal expected from the coil sequences of uninfluenced secondary coils is hardly achievable, at least not without additional costly balancing measures.
Therefore, it is an object of this invention to provide an angle sensor according to the introductory paragraph above whose structure is uncomplicated and inexpensive and which achieves a high degree of measuring accuracy without expensive balancing measures. Specifically, an inductive angle sensor according to this invention should be as insensitive to manufacturing and mounting tolerances as possible, as well as to environmental influences, particularly outside temperature.